发布日期: 2019-05-27

文章字数: 1.7k

阅读时长: 8 分

阅读次数:

#1.第一个程序

/*编写字节码文件*/

package Unit1;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

public class a_ServerletDemo implements Servlet{

    private static final String HttpServletResponse = null;

    @Override
    public void destroy() {
        /*
         * 销毁时调用
         * */

    }

    @Override
    public ServletConfig getServletConfig() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public String getServletInfo() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
        /*
         * 创建Servlet调用
         * */
    }

    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        System.out.println("Browser: I send you a message!"); //打印终端
        /*
         * 每一次发送请求的时候就会调用
         * */

        HttpServletResponse resp = (HttpServletResponse)res;
        resp.getWriter().write("<h1>Server:I send a message</h1>"); //返回信息到浏览器
    }

}

<!-- #添加映射 -->
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>FirstTry</display-name>


  <!-- 自定义信息 -->
  <servlet>
      <servlet-name>Tashi</servlet-name>
      <servlet-class>Unit1.a_ServerletDemo</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>Tashi</servlet-name>
      <url-pattern>/d</url-pattern>
  </servlet-mapping>

  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
</web-app>

#2.获取字节码文件

Class c = Class.forName("获取字节码.Person");
System.out.println(c);

Class c2 = Person.class;
System.out.println(c2);


Person p = new Person();
Class c3 = p.getClass();
System.out.println(c3);

#3.通过字节码创建对象

public class Main{
    Class c = Class.forName("......");
    Person p = (Person)c.newInstance();
    p.show(); //调用P的show方法


    {
        //2. 通过有参的构造器来创建对象
        Constructor ah = c.getConstructor(String.class, Integer.class);
        Person p = (Person)ah.newInstance("鲁班",18);
        p.show();
    }
}

#4.获取字段

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;

public class Main {
    public static void main (String[] args)throws  Exception{
        Class c = Class.forName("获取字节码.Person");
        {
            /*获取公共字段*/
            //1.获取字节码  必须设置public 才可以
            Person per = (Person)c.newInstance();
            Field f = c.getField("name");
            f.set(per,"张三");
            per.show();
        }
        {
            /*获取私有字段*/
            Person per = (Person)c.newInstance();

            //暴力反射获取字段
            Field f = c.getDeclaredField("age");

            //去除私有权限
            f.setAccessible(true);

            f.set(per, 666);

            per.show();
        }
    }
}

#5.获取方法

import java.lang.reflect.Method;

public class Main {
    public static void main(String[] args)throws  Exception{
        Class c = Class.forName("获取字节码.Person");

        {
            /*获取公共方法*/
            Person per = (Person)c.newInstance();

            Method m = c.getMethod("show");//获取方法
            System.out.println(m.getName());//打印方法名字
            m.invoke(per); //执行方法  参数传入对象
        }

        {
            /*获取私有方法*/
            Person p = (Person)c.newInstance();

            Method m = c.getDeclaredMethod("temp");
            m.setAccessible(true);
            m.invoke(p);

        }

    }
}

Servlet

Servlet是一个基于Java技术的Web组件，运行在服务端

Servlet生命周期

装载
创建实例
调用init方法init()
服务service()
销毁destory()

#注解的方式创建servlet

src -> new -> Servlet

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/Demo")
public class Demo extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Get Message");
    }
}


// http://localhost:8080/Demo

#`doGet`与`doPost`

public class Main extends HttpServlet {
    //每次请求的时候就会调用此方法
    // 注意：一但写了service就不会去找doGet与doPost
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("请求");
    }
    //get请求会调用这个方法
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Get请求");
    }
    //post请求会调用这个方法
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Post请求");
    }
}

内部原理

HttpServlet是专门负责处理http请求与响应的。HttpServlet接口继承GenericServlet接口继承 Servlet接口

当收到一个请求的时候，就会找到service方法,如果不存在就会在它的父类中找，强制转换httpServlet,获取请求的方式，然后调用get还是post

1.获取请求参数

req.getParameter("userName");

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    String mesg = req.getParameter("mesg"); //获取前端的表单
    System.out.println(mesg);
}

#ServletContext

WEB应用的上下文对象

生命周期

服务器创建与服务器关闭

如何获取

全局初始化参数

public void init(...){
    ServletContext sc = config.getServletContext();
    System.out.println(sc);
}

public void init(...){
    super.init(config);
}

public void service(...){
    ServletContext context = this.getServletContext();
    System.out.println(context);
}

获取绝对地址

String str = context.getRealPath('filePath ');

#响应`response`

设置响应行|响应头|响应体

设置响应行

@Override
  protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      // 设置状态码
      resp.setStatus(200);
  }

设置响应头
- add设置
  - addHeader(String name, String value);
  - addIntHeader(String name, int value);
  - addDateHeader(String name, date);
- set修改
  - setHeader("Name", "LLE");

@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // 设置状态码
    resp.setStatus(200);
    // 设置响应头
    resp.addHeader("Name", "Tashi");
    resp.addIntHeader("Age", 20);
    resp.addDateHeader("Birthday",new Date().getTime());
}

重定向

// 设置响应头
resp.setStatus(302);

// 设置响应头
resp.setHeader("location", "/book");

resp.sendRedirect("/book");

定时刷新重定向

resp.setHeader("refresh", "3;url=/book");

设置相应体
- 通过writter方法
- 通过OutPutStream来写

// 如果有html标签会自动解析
 @Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    resp.setCharacterEncoding("UTF-8");
    resp.setHeader("Content-Type", "text/html;charset=UTF-8"); //或者 resp.setContentType("text/html;charset=UTF-8");
    resp.getWriter().write("<h1>Yo!啊哈</h1>");
}

 @Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    String path = this.getServletContext().getRealPath("index.jsp");
    //加载文件
    FileInputStream in = new FileInputStream(path);
    ServletOutputStream out = resp.getOutputStream(); //输出流

    //获取字节码
    byte[] buffer = new byte[1024];
    int len = 0;
    while((len=in.read(buffer))!= -1) {
        System.out.println(len);
        System.out.println(Arrays.toString(buffer));
        out.write(buffer,0,len); // 写给浏览器
    }

    //关闭输入流
    in.close();
}

#请求`request`

设置编码格式req.setCharacterEncoding("UTF-8");

获取请求行

System.out.println(req.getMethod()); //请求的方法
System.out.println(req.getRequestURL()); //请求的URL
System.out.println(req.getRequestURI()); //请求的URI
System.out.println(req.getQueryString()); //请求的参数
System.out.println(req.getContextPath());// 请求当前的Web应用名称

获取请求头的名称

Enumeration<String> headerNames = req.getHeaderNames();
while(headerNames.hasMoreElements()){
  String name = headerNames.nextElement();
  System.out.println(name+"\t"+ req.getHeader(name));
}

获取请求体

//请求一个
String str1 = req.getParameter("Fruit");
System.out.println(str1);

//请求多个
String[] str2 = req.getParameterValues("Fruit");
System.out.println(Arrays.toString(str2));

//请求所有参数名称
Enumeration<String> parameterNames = req.getParameterNames();
while(parameterNames.hasMoreElements()){
    String name = parameterNames.nextElement();
    System.out.println(name);
}

//获取所有参数值
Map<String, String[]> parameterMap = req.getParameterMap();
for(Map.Entry<String,String[]>entry: parameterMap.entrySet()){
    System.out.println(entry.getKey());
    System.out.println(Arrays.toString(entry.getValue()));
}

#请求转发与重定向

1.获取转发器req.getRequestDispatcher('path')
2.转发disp.forward(request,response)

#Demo

文件下载

 @Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //接收参数
    String  name = req.getParameter("Main.mp4");
    String mType = this.getServletContext().getMimeType(name);

    resp.setContentType(mType); //设置类型
    resp.setHeader("Content-Disposition", "attachment;filename="+name); //告诉浏览器以附件形式

    //获取文件路径
    String path = this.getServletContext().getRealPath("Download/"+name);

    //获取响应的输出
    ServletOutputStream out = resp.getOutputStream();


    //加载文件
    FileInputStream in = new FileInputStream(path);
    byte[] buffer = new byte[1024];
    int len = 0;
    while((len = in.read())!=-1){
        out.write(buffer,0, len);
    }
    in.close();
}